It is known to provide the door, the door frame or other parts of the side wall of an automotive vehicle with one or more impact girders designed, by controlled deformation, to take up at least a portion of the energy of an impact applied to a side of the vehicle, e.g. a lateral collision.
Reference may be had in that regard to the commonly owned U.S. Pat. No. 4,915,442 issued Apr. 10, 1990. The girder profiles or structural shapes which have been used heretofore for this purpose, have been tube structures, I-beam profiles, II-beam profiles or other hollow structural shapes. The girder can be composed of metal and can be located along the side of the vehicle, generally at a level of a bumper of a vehicle which might be expected to impact on the side of the vehicle provided with the impact girder. The impact girder can be mounted at its ends on the vehicle body, for example, on parts of the door frame when the impact girder is to be provided in the door of the vehicle. In the case of impact girders which are located in a side wall region other than a door, the impact girder can be affixed at its ends to the struts, braces or other parts of the vehicle body itself.
To maximize the deformation work and thus attenuate the impact to the greatest possible degree and thereby protect the occupants of the vehicle against the lateral impact, the deformation resistance of the impact girder should be only slightly smaller than that of the frame or door construction in which the impact girder is incorporated.
During a collision process, however, before complete deformation of the structure, the resistance to deformation of the impact girder should not be so high that the supporting beams or frame parts will be deformed or the impact girder torn from the body of the vehicle.
The customary impact girders show an increased resistance to deformation during the deformation process. As a consequence, the resistance to deformation cannot at the start of such deformation be only slightly smaller than the deformation resistance of the supporting beams and frame parts. Hence the initial resistance to deformation of the impact girder may be substantially smaller than is desirable. It is also desirable to provide an impact girder whose resistance force or resistance to deformation is approximately constant over the total deformation stroke of the impact girder.